Color variation in printed materials can be a major source of dissatisfaction with users of color printers. Color variation occurs when a particular color appears in a printed document at a color value that is more or less than a desired target value for that color. A major source of color variation is inconsistent and/or improper amounts of colorant present on the printed document. Current printers attempt to maintain color variation tolerances within desired thresholds for printed materials through the use of calibration systems.
Current printers are unable to consistently maintain color variation tolerances within desired thresholds in printed materials without the use of expensive and cumbersome calibration systems. Some of these systems involve manual interaction by a user of a printing device. For example, sheets of paper may need to be fed through the printing device feeder while the device generates test patterns on a printable media. Such calibration processes are disruptive and delay printing because they are normally performed between print jobs which interrupts printing performance. Such calibration techniques are also costly because sheets of paper are used to perform the closed loop calibration. Consequently, calibration processes involving manual interaction are usually performed infrequently over longer periods of time, and only after noticeable color value drifts in documents.
Other calibration processes include testing on some type of a test element, such as a transfer belt, which is internal to a printing device. Using a transfer belt to perform a calibration process, however, is prone to inaccuracies because results obtained from measuring colorant levels applied to a transfer belt may vary significantly from actual color values output by a printing device on printed material. There can be measurable differences between colorants printed on a calibration element when compared to the colorants printed on a printable media that is output by the printing device. Moreover, internal calibration processes usually rely on static parameters established at a time when a printing device is manufactured and do not account for behavior differences associated with the printing device over time. The behavior differences can be caused by many factors, such as environmental fluctuations (e.g., temperature, atmospheric pressure, humidity, etc.), different types of print media, different types of ink, and/or changes to print elements due to wear.
When identical documents are produced by more than one printer and compared to each other, there may be significant and noticeable color value variations for identical colors used to print the documents. Even identical printer models may operate differently from each other which causes them to sense and print colorants at different variations with respect to each other. Identical printer models may print different color variations because their respective components usually contain inherent operating differentials.
This is especially problematic when cluster printing which involves using a plurality of printers that operate as a single virtual printer to print multiple pages of a print job. For example, a print job request can be divided and distributed to four printers that are clustered together and which act as a single virtual printer. The virtual printer performs four times faster than each of the four printers individually and provides scalability. However, the printed output will not appear to have been produced by a single continuous printer if the colorant levels produced by each of the printers are not exactly alike. This could be especially pronounced if one of the colors used in the printed documents appears throughout the documents as a prominent feature, such as a logo. For example, the logo may appear to be cherry red on one page, yet appear to be fire red on another page.
Another problem is presented when attempting to print documents at different sites, or locations. It may be desirable for the printers to produce documents with consistent color values despite being at different locations. Currently, however, there is no reasonable and inexpensive system to ensure that the different printers produce the same printed documents with imperceptible color value variations between them.